Field of the Invention
The present invention relates, in general, to a geothermal power generation system and method using heat exchange between working gas and molten salt, and more particularly, to a geothermal power generation system and method in which working gas undergoes heat exchange in the ground.
Description of the Related Art
Geothermal power generation is a type of power generation that generates electricity by accepting heat in the form of steam or hot water from a hot subterranean layer. Subterranean heat is a type of energy that is contained in hot water, hot rocks or the like found underground in regions ranging from relatively shallow regions to regions located several kilometers beneath the surface of the Earth.
When hot steam is obtained from these underground regions, the hot steam is introduced to a steam turbine to rotate the turbine at a high speed, so that a power generator connected to the turbine generates electricity. If the steam which erupts from underground contains only a small amount of moisture, it can be sent directly to the turbine. If the steam erupts along with a large amount of hot water, the hot water is sent to a heat exchanger in which the water is vaporized and is then sent to the turbine as steam. In addition, when water has a low temperature, a liquid that has a lower boiling point is vaporized and is then sent to the turbine.
Geothermal power generation does not need fuel in principle and is a clean energy source that is free from pollution attributable to the combustion of fuel. However, noncondensable gas that erupts from a geothermal well contains a small amount of hydrogen sulfide. The eruption of hydrogen sulfide is not problematic at present since the concentration of hydrogen sulfide is low and below environmental standards. However, desulfurization equipment will be required if a large amount of hydrogen sulfide erupts in the future. In addition, after power generation, all of the hot water is returned to the underground region from whence it came since it contains a small amount of arsenic. However, if an economical dearsenic technology is established, the hot water will also be usable after power generation as a valuable low-temperature thermal energy resource.
The majority of costs for geothermal power generation include a cost for construction of a geothermal power plant and a cost for excavation of a geothermal well. The costs for geothermal power generation vary depending on the quality and type of geothermal power generation. Geothermal power generation has an advantage of economic competitiveness, although a typical geothermal power plant has a smaller scale than a thermal power plant or an atomic power plant. Geothermal power generation is also characterized as a small and locally-distributed energy source.
FIG. 1 a schematic view showing the configuration of a geothermal power generation system using high-temperature and high-pressure compressed air.
In an example, Korean Patent Application No. 10-2010-0115466 introduces a geothermal power generation system using high-temperature and high-pressure compressed air. As shown in FIG. 1, in the system of this application, a cooling unit which reduces temperature is removed from a rear end of a compressor 4, and artificial geothermal power generation is carried out using the characteristic of high-temperature and high-pressure compressed air that is produced by the compressor 4. In this fashion, the efficiency of the power generation using the compressed air can be improved.
FIG. 2 is a schematic view showing the configuration of a geothermal power generation system of the related art.
In addition, Korean Patent Application No. 10-2010-0063987 introduces a low-temperature geothermal power generation system. As shown in FIG. 2, the geothermal power generation system of this application includes a superheater 20, a post pressure pump 40 and a preheater 60 in order to carry out geothermal power generation using geothermal water having a temperature of 100° C. or less. In this system, it is possible to increase the efficiency of a carburetor 4 by increasing the temperature and enthalpy of secondary fluid by a predetermined degree by actuating the preheater 60 using the remaining heat of geothermal water that is supplied from the carburetor 4, increase pressure by increasing the temperature of the secondary fluid that is vaporized by the superheater 20, and increase the efficiency of the carburetor and maintain the flow rate of the superheater 20 by increasing the pressure of the secondary fluid that is introduced into a turbine 6 by the post pressure pump 40 and decreasing the pressure of the superheater 20. Therefore, this system can effectively generate electricity using geothermal water that has a relatively low temperature.
In geothermal power generation, hot water or steam that has been drawn up from underground is not renewable energy in the strictest sense. Since the amount of subterranean heat that leaks during geothermal power generation is greater than the recharging capacity of a reservoir, the amount of heat stored beneath the surface of the Earth is currently reducing. Although it will take a long time, when subterranean hot water or steam is exhausted and hot rock layers are cooled, no heat can be drawn up from underground any longer. It is necessary to convert other types of energy into geothermal energy which can be used for geothermal power generation. Working gas such as carbon dioxide (CO2) can be used for geothermal power generation since it does not easily react with substances in the ground unlike water and can more effectively transfer heat stored in the rock bed through cracks in the ground.